JP6800640B2 - Wide-angle lens - Google Patents

Description

The present invention relates to a wide-angle lens used for an intercom or the like of a front door.

As lenses to be mounted on surveillance cameras, in-vehicle cameras, cameras for portable devices, etc., a lens with 3 elements in 3 groups in which the 1st lens, the 2nd lens, the aperture, and the 3rd lens are arranged in order from the object side is proposed. Has been done. In such a wide-angle lens, a plastic lens having a relatively high refractive index is used for all of the first lens, the second lens, and the third lens in order to reduce the cost and thickness (see Patent Document 1). ). Further, as the second lens, a biconvex lens having convex lens surfaces on both the object side and the image side is used.

Japanese Unexamined Patent Publication No. 2014-209190

Since a lens having a high refractive index tends to have a small Abbe number, if a plastic lens having a high refractive index is used for the biconvex second lens such as the wide-angle lens described in Patent Document 1, the second lens can be used. The dispersion is large. On the other hand, a wide-angle lens used for an intercom or the like of a front door is required to have a high resolution in the central portion, and thus to have a small axial chromatic aberration. However, in the wide-angle lens described in Patent Document 1, there is a limit to the demand for improving the resolution of the central portion.

In view of the above problems, an object of the present invention is to provide a wide-angle lens capable of improving axial chromatic aberration.

In order to solve the above problems, the wide-angle lens according to the present invention includes a first lens, a second lens, an aperture, and a third lens arranged in order from the object side, and the first lens has at least one surface. Is an aspherical lens with a convex surface facing the object side, and the second lens is a positive meniscus lens having an aspherical surface at least one surface and a convex surface facing the image side. Is a positive lens having at least one surface that is aspherical, with a convex surface facing the object side and a convex surface facing the image side, the abbe number of the first lens is ν1, and the abbe number of the second lens is ν2. When the Abbe number of the third lens is ν3, the Abbe numbers ν1, ν2, and ν3 all exceed 50, and the center of the lens surface located on the object side of the first lens and the second lens. When the distance from the center of the lens surface located on the image side is da (mm), the distance da is the following conditional expression.
1 <da / f0≤3.226
It is characterized by satisfying .

In the present invention, the Abbe number ν1 of the first lens, the Abbe number ν2 of the second lens, and the Abbe number ν3 of the third lens all exceed 50, so that the color dispersion is small. Moreover, since the second lens is a meniscus lens, axial chromatic aberration is canceled out between the surface on the object side and the surface on the image side. Therefore, the axial chromatic aberration of the wide-angle lens can be improved. Therefore, it is possible to realize a wide-angle lens having a high resolution in the central portion, such as a wide-angle lens used for an intercom of a front door. According to this aspect, since da / f0 is 3.226 or less, astigmatism can be easily corrected. Further, since da / f0 exceeds 1, the size of the optical lens in the optical axis direction can be shortened.

In the present invention, the radius of curvature at the center of the lens surface located on the image side of the first lens is R12 (mm), and the radius of curvature at the center of the lens surface located on the object side of the second lens is R21 (mm). When the total focal length is f0 (mm) and the lens surface is a convex surface protruding toward the object side or a concave surface concave toward the object side, the radius of curvature R
When 12 and the radius of curvature R21 are positive values and the lens surface is a convex surface protruding toward the image side or a concave surface concave toward the image side, when the radius of curvature R12 and the radius of curvature R21 are negative values, The radius of curvature R12, the radius of curvature R21, and the total focal length f0 are given by the following conditional expression −5 <(R12 × R21) / f0 <-2.
A mode that satisfies the above conditions can be adopted. According to such an aspect, astigmatism can be reduced.

In the present invention, both the second lens and the third lens can adopt an aspect in which both the lens surface located on the object side and the lens surface located on the image side are aspherical surfaces. According to this aspect, since the lens shape is appropriate, aberration can be reduced.

In the present invention, an embodiment in which the horizontal angle of view is less than 100 deg can be adopted. Since it is not necessary to make the angle of view extremely large in the wide-angle lens used for the intercom of the entrance door, it is possible to realize a wide-angle lens having a high resolution in the central portion.

In the present invention, the Abbe number ν1 of the first lens, the Abbe number ν2 of the second lens, and the Abbe number ν3 of the third lens all exceed 50, so that the color dispersion is small. Moreover, since the second lens is a meniscus lens, axial chromatic aberration is canceled out between the surface on the object side and the surface on the image side. Therefore, the axial chromatic aberration of the wide-angle lens can be improved. Therefore, it is possible to realize a wide-angle lens having a high resolution in the central portion, such as a wide-angle lens used for an intercom of a front door.

It is sectional drawing of the lens unit provided with the wide-angle lens which concerns on Embodiment 1 of this invention. It is explanatory drawing of the wide-angle lens shown in FIG. It is explanatory drawing which shows the aberration characteristic of the wide-angle lens shown in FIG. It is explanatory drawing of the wide-angle lens which concerns on Embodiment 2 of this invention. It is explanatory drawing which shows the aberration characteristic of the wide-angle lens shown in FIG. It is explanatory drawing of the wide-angle lens which concerns on Embodiment 3 of this invention. It is explanatory drawing which shows the aberration characteristic of the wide-angle lens shown in FIG.

Hereinafter, examples of a wide-angle lens to which the present invention is applied will be described with reference to the drawings.

[Embodiment 1]
FIG. 1 is a cross-sectional view of a lens unit 200 provided with a wide-angle lens 100 according to a first embodiment of the present invention. 2A and 2B are explanatory views of the wide-angle lens 100 shown in FIG. 1, and FIGS. 2A, 2B, and 2C are explanatory views showing a lens configuration, explanatory views showing spherical aberration, and chromatic aberration of magnification, respectively. It is explanatory drawing which shows. FIG. 3 is an explanatory diagram showing the aberration characteristics of the wide-angle lens shown in FIG. 1, and FIGS. 3 (a), (b), and (c) show explanatory views showing astigmatism and the like, and lateral aberration, respectively. It is explanatory drawing. In addition, in showing each surface 1-9 in FIG. 2A, "*" is attached to the aspherical surface. 2 (b), (c) and 3 (a) show aberrations in red light R (wavelength 486 nm), green light G (wavelength 588 nm), and blue light B (wavelength 656 nm). 2 (b) shows spherical aberration when the pupil diameter (Pupil Radius) is 0.4798 mm, and FIG. 2 (c) shows the chromatic aberration of magnification in the maximum field. In FIG. 3A, S is attached to the characteristic in the sagittal direction, and T is attached to the characteristic in the tangier direction. Further, the distortion shown in FIG. 3A indicates the rate of change of the image in the central portion and the peripheral portion of the image pickup, and the smaller the absolute value of the numerical value representing the distortion, the higher the accuracy of the lens. FIG. 3B shows lateral aberrations in two directions (y direction and x direction) orthogonal to the optical axis at angles of 0.00 deg, 12.11 deg, 23.90 deg, 34.18 deg, 46.03 deg, and 56.64 deg. Is shown. The same applies to FIGS. 4 to 7 described later.

As shown in FIG. 1, the lens unit 200 of this embodiment includes a wide-angle lens 100 having a lens configuration of three elements in three groups and a lens holder 210 for holding the wide-angle lens 100. The wide-angle lens 100 has a first lens 10, a second lens 20, an aperture 40, and a third lens 30 arranged in order from the object side, and has an infrared filter or the like on the image side with respect to the third lens 30. A flat plate-shaped filter 50 and an image pickup element 60 are arranged. The lens holder 210 has an annular bottom plate portion 211 for holding the filter 50 and a tubular portion 212 extending from the bottom plate portion 211 to the object side, and the wide-angle lens 100 is arranged inside the tubular portion 212. There is. A screw groove 215 for fixing the lens unit 200 to the optical device is formed on the outer peripheral surface of the tubular portion 212. In the present embodiment, when the wide-angle lens 100 is provided inside the tubular portion 212, an annular spacer 70 is arranged between the second lens 20 and the aperture 40, and in this state, an annular spacer 70 formed inside the tubular portion 212. The convex portion 213 is crimped so as to cover the outer peripheral end portion of the first lens 10 from the object side.

As shown in FIG. 2, in the wide-angle lens 100, the first lens 10 is a negative meniscus lens in which at least one surface is aspherical and the convex surface is directed toward the object side. The second lens 20 is a positive meniscus lens in which at least one surface is aspherical and the convex surface is directed toward the image side. The third lens 30 is a positive lens in which at least one surface is aspherical and the convex surface is directed toward the image side.

In the present embodiment, in the first lens 10, the surface on the object side (first surface 1) is a convex surface of a spherical surface, and the surface on the image side (second surface 2) is a concave surface on an aspherical surface. In the second lens 20, the surface on the object side (third surface 3) is an aspherical concave surface, and the surface on the image side (fourth surface 4) is an aspherical convex surface. In the third lens 30, the surface on the object side (sixth surface 6) is an aspherical convex surface, and the surface on the image side (seventh surface 7) is an aspherical convex surface. In this embodiment, the first lens 10, the second lens 20, and the third lens 30 are all made of plastic lenses made of acrylic resin, polycarbonate, polyolefin, or the like. The diaphragm 40 constitutes the fifth surface 5, the object-side surface of the filter 50 constitutes the eighth surface 8, and the image-side surface of the filter 50 constitutes the ninth surface 9.

Table 1 shows the characteristics of the wide-angle lens 100 configured in this way, the physical properties of each surface, and the aspherical coefficient.

The following items are shown in the first column of Table 1. The same applies to Tables 2 and 3 described later.
Focal length f0 (Effective Focal Length) of the entire lens system
Distance between objects (Total Track)
F value of the entire lens system (Image Space F / #)
Max. Field Angle
Horizontal Field Angle

The following items on each side are shown in the second column of Table 1. The unit of radius of curvature, thickness, and focal length is mm. Here, when the lens surface is a convex surface protruding toward the object side or a concave surface recessed toward the object side, the radius of curvature is set to a positive value, and the lens surface is a convex surface or an image protruding toward the image side. In the case of a concave surface that is recessed toward the side, the radius of curvature is set as a negative value. The same applies to Tables 2 and 3 described later.
Radius of curvature (Radius)
Thickness
Refractive index Nd
Abbe number νd
Focal length f

In the third and fourth columns of Table 1, the aspherical coefficients A4, A6, A8, and A10 when the shape of the aspherical surface is expressed by the following equation (Equation 1) among the surfaces are shown. In the following equation, the sag amount (axis in the optical axis direction) is z, the height in the direction perpendicular to the optical axis (ray height) is r, the conical coefficient is k, and the reciprocal of the radius of curvature is c. The same applies to Tables 2 and 3 described later.

As shown in Table 1, in the wide-angle lens 100 of this embodiment, the focal length f0 of the entire lens system is 2.114 mm, the distance between objects is 15.235 mm, and the F value of the entire lens system is 2. The maximum angle of view is 113 deg, and the horizontal angle of view is less than 100 deg (92 deg).

The wide-angle lens 100 satisfies all of the following conditions (1), (2), and (3). First, as condition (1), when the Abbe number of the first lens 10 is ν1, the Abbe number of the second lens 20 is ν2, and the Abbe number of the third lens 30 is ν3, the Abbe numbers ν1, ν2, ν3 Are all over 50. More specifically, first, the first lens 10 has an Abbe number ν1 of 58.0 and a refractive index of Nd of 1.491. The second lens 20 has an Abbe number ν2 of 55.8 and a refractive index of Nd of 1.531. The third lens 30 has an Abbe number ν3 of 55.8 and a refractive index of Nd of 1.531. Therefore, the Abbe number and the refractive index satisfy the following conditions.
Abbe number 1st lens 10> 2nd lens 20 = 3rd lens 30> 50
Refractive index Nd
1st lens 10 <2nd lens 20 = 3rd lens 30

Further, the radius of curvature at the center of the lens surface (second surface 2) located on the image side in the first lens 10 is R12 (mm), and the lens surface (third surface 3) located on the object side in the second lens 20. When the radius of curvature at the center of the lens is R21 (mm) and the total focal length is f0 (mm), the radius of curvature R12, the radius of curvature R21, and the total focal length f0 satisfy the following condition (2). There is.
Condition (2): -5 <(R12 x R21) / f0 <-2

More specifically, the radius of curvature R12 at the center of the lens surface (second surface 2) located on the image side in the first lens 10 is 1.970 mm, and the lens surface located on the object side in the second lens 20 (second surface 2). Since the radius of curvature R21 at the center of the third surface) is -3.937 (mm) and the total focal length f0 is 2.114 mm, (R12 × R21) / f0 is -3.67. The above condition (2) is satisfied.

Further, the distance between the center of the lens surface (first surface 1) located on the object side of the first lens 10 and the center of the lens surface (fourth surface 4) located on the image side of the second lens is da (mm). When the distance da is 6.65 mm, the following condition (3) is satisfied.
Condition (3): 1 <da / f0 ≤ 3.226
Meet.

As described above, the wide-angle lens 100 of this embodiment has a lens configuration of three elements in three groups, and the three lenses are made of plastic. Therefore, the cost of the wide-angle lens 100 can be reduced and the weight can be reduced. Further, in the present embodiment, the Abbe number ν1 of the first lens 10, the Abbe number ν2 of the second lens 20, and the Abbe number ν3 of the third lens 30 all exceed 50, satisfying the condition (1). Therefore, the color dispersion is small. Moreover, the second lens 20 is a meniscus lens, and in the second lens 20, axial chromatic aberration is canceled by the surface on the object side (third surface 3) and the surface on the image side (fourth surface 4). Therefore, as shown in FIG. 2, the axial chromatic aberration of the wide-angle lens 100 is small. Therefore, the wide-angle lens 100 is used as an optical system that is required to have a high resolution in the central portion in an optical system that does not require an extremely large angle of view, such as an optical system used for an intercom of a front door. Are suitable.

Further, the radius of curvature R12 (mm) at the center of the lens surface (second surface 2) located on the image side of the first lens 10 and the center of the lens surface (third surface 3) located on the object side of the second lens 20. The radius of curvature R21 (mm) and the total focal length f0 (mm) in the above condition (2) are satisfied. Therefore, as shown in FIG. 3, astigmatism is canceled out between the image-side surface (second surface 2) of the first lens 10 and the object-side surface (third surface 3) of the second lens 20. .. Therefore, the astigmatism of the wide-angle lens 100 can be reduced.
Condition (2): -5 <(R12 x R21) / f0 <-2

That is, when (R12 × R21) / f0 is -5 or less, or -2 or more, the astigmatism of the wide-angle lens 100 tends not to be sufficiently reduced. In order to reduce the amount, it is preferable that the radii of curvature R12 and R21 satisfy the condition (2).

Further, the distance da (mm) between the center of the lens surface (first surface 1) located on the object side in the first lens 10 and the center of the lens surface (fourth surface 4) located on the image side in the second lens is Condition (3) is satisfied. Therefore, since da / f0 is 3.226 or less , astigmatism can be easily corrected. Further, since da / f0 exceeds 1, the dimension (distance between objects) of the wide-angle lens 100 in the optical axis direction can be shortened.

Further, since both the second lens 20 and the third lens 30 are aspherical on both sides, aberrations such as spherical aberration can be reduced.

[Embodiment 2]
4A and 4B are explanatory views of a wide-angle lens 100 according to a second embodiment of the present invention, and FIGS. 4A, 4B, and 4C are explanatory views showing a lens configuration and explanatory views showing spherical aberration, respectively. It is a figure and the explanatory view which shows the chromatic aberration of magnification. 5A and 5B are explanatory views showing the aberration characteristics of the wide-angle lens shown in FIG. 4, and FIGS. 4A, 4B, and 4C show explanatory views showing astigmatism and the like, and lateral aberrations, respectively. It is explanatory drawing. FIG. 5B shows lateral aberrations in two directions (y direction and x direction) orthogonal to the optical axis at angles of 0.00 deg, 12.09 deg, 23.88 deg, 35.17 deg, 46.00 deg, and 56.44 deg. Is shown.

As shown in FIG. 4, the wide-angle lens 100 of the present embodiment also has the first lens 10, the second lens 20, the aperture 40, and the third lens 30 arranged in order from the object side, as in the first embodiment. ing. The first lens 10 is a negative meniscus lens in which at least one surface is aspherical and a convex surface is directed toward an object. The second lens 20 is a positive meniscus lens in which at least one surface is aspherical and the convex surface is directed toward the image side. The third lens 30 is a positive lens in which at least one surface is aspherical and the convex surface is directed toward the image side.

In the present embodiment, as in the first embodiment, the surface on the object side (first surface 1) of the first lens 10 is a spherical convex surface, and the surface on the image side (second surface 2) is an aspherical concave surface. is there. In the second lens 20, the surface on the object side (third surface 3) is an aspherical concave surface, and the surface on the image side (fourth surface 4) is an aspherical convex surface. In the third lens 30, the surface on the object side (sixth surface 6) is an aspherical convex surface, and the surface on the image side (seventh surface 7) is an aspherical convex surface. In this embodiment, the first lens 10, the second lens 20, and the third lens 30 are made of plastic lenses. The diaphragm 40 constitutes the fifth surface 5, the object-side surface of the filter 50 constitutes the eighth surface 8, and the image-side surface of the filter 50 constitutes the ninth surface 9.

Table 2 shows the characteristics of the wide-angle lens 100 configured in this way, the physical properties of each surface, and the aspherical coefficient.

As shown in Table 2, in the wide-angle lens 100 of this embodiment, the focal length f0 of the entire lens system is 2.120 mm, the distance between objects is 15.072 mm, and the F value of the entire lens system is 2. The maximum angle of view is 113 deg, and the horizontal angle of view is less than 100 deg (92 deg).

Further, the wide-angle lens 100 satisfies all of the following conditions (1), (2), and (3). First, as the condition (1), the Abbe number ν1 of the first lens 10, the Abbe number ν2 of the second lens 20, and the Abbe number ν3 of the third lens 30 all exceed 50. More specifically, first, the first lens 10 has an Abbe number ν1 of 58.0 and a refractive index of Nd of 1.491. The second lens 20 has an Abbe number ν2 of 55.8 and a refractive index of Nd of 1.531. The third lens 30 has an Abbe number ν3 of 55.8 and a refractive index of Nd of 1.531. Therefore, the Abbe number and the refractive index satisfy the following conditions.
Abbe number 1st lens 10> 2nd lens 20 = 3rd lens 30> 50
Refractive index Nd
1st lens 10 <2nd lens 20 = 3rd lens 30

Further, the radius of curvature R12 (mm) at the center of the lens surface (second surface 2) located on the image side of the first lens 10 and the center of the lens surface (third surface 3) located on the object side of the second lens 20. The radius of curvature R21 (mm) and the focal length f0 in the above satisfy the following condition (2).
Condition (2): -5 <(R12 x R21) / f0 <-2

More specifically, the radius of curvature R12 at the center of the lens surface (second surface 2) located on the image side in the first lens 10 is 2.133 mm, and the lens surface located on the object side in the second lens 20 (second surface 2). Since the radius of curvature R21 at the center of the third surface 3) is -3.690 (mm) and the total focal length f0 is 2.120 mm, (R12 × R21) / f0 is -3.71. , The above condition (2) is satisfied.

Further, the distance between the center of the lens surface (first surface 1) located on the object side of the first lens 10 and the center of the lens surface (fourth surface 4) located on the image side of the second lens is da (mm). When the distance da is 6.84 mm, the following condition (3) is satisfied.
Condition (3): 1 <da / f0 ≤ 3.226
Meet.

As described above, the wide-angle lens 100 of this embodiment has a lens configuration of three elements in three groups, and the three lenses are made of plastic. Therefore, the cost of the wide-angle lens 100 can be reduced and the weight can be reduced. Further, the Abbe number ν1 of the first lens 10, the Abbe number ν2 of the second lens 20, and the Abbe number ν3 of the third lens 30 all exceed 50, and the condition (1) is satisfied. The variance is small. Moreover, since the second lens 20 is a meniscus lens, the axial chromatic aberration is canceled by the surface on the object side (third surface 3) and the surface on the image side (fourth surface 4) in the second lens 20. Therefore, the same effect as that of the first embodiment is obtained, such as the small axial chromatic aberration of the wide-angle lens 100.

[Embodiment 3]
FIG. 6 is an explanatory view of the wide-angle lens 100 according to the third embodiment of the present invention, and FIGS. 6A, 6B, and 6C are explanatory views showing a lens configuration and explanatory views showing spherical aberration, respectively. It is a figure and the explanatory view which shows the chromatic aberration of magnification. 7 is an explanatory diagram showing the aberration characteristics of the wide-angle lens shown in FIG. 6, and FIGS. 4A, 4B, and 4C show explanatory views showing astigmatism and the like, and lateral aberration, respectively. It is explanatory drawing. FIG. 7B shows lateral aberrations in two directions (y direction and x direction) orthogonal to the optical axis at angles of 0.00 deg, 12.12 deg, 23.91 deg, 35.18 deg, 46.00 deg, and 56.55 deg. Is shown.

As shown in FIG. 6, the wide-angle lens 100 of the present embodiment also has the first lens 10, the second lens 20, the aperture 40, and the third lens 30 arranged in order from the object side, as in the first embodiment. ing. The first lens 10 is a negative meniscus lens in which at least one surface is aspherical and a convex surface is directed toward an object. The second lens 20 is a positive meniscus lens in which at least one surface is aspherical and the convex surface is directed toward the image side. The third lens 30 is a positive lens in which at least one surface is aspherical and the convex surface is directed toward the image side.

In the present embodiment, as in the first embodiment, the surface on the object side (first surface 1) of the first lens 10 is a spherical convex surface, and the surface on the image side (second surface 2) is an aspherical concave surface. is there. In the second lens 20, the surface on the object side (third surface 3) is an aspherical concave surface, and the surface on the image side (fourth surface 4) is an aspherical convex surface. In the third lens 30, the surface on the object side (sixth surface 6) is an aspherical convex surface, and the surface on the image side (seventh surface 7) is an aspherical convex surface. In this embodiment, the first lens 10, the second lens 20, and the third lens 30 are made of plastic lenses. The diaphragm 40 constitutes the fifth surface 5, the object-side surface of the filter 50 constitutes the eighth surface 8, and the image-side surface of the filter 50 constitutes the ninth surface 9.

Table 3 shows the characteristics of the wide-angle lens 100 configured in this way, the physical properties of each surface, and the aspherical coefficient.

As shown in Table 3, in the wide-angle lens 100 of this embodiment, the focal length f0 of the entire lens system is 2.112 mm, the distance between objects is 15.185 mm, and the F value of the entire lens system is 2. The maximum angle of view is 113 deg, and the horizontal angle of view is less than 100 deg (92 deg).

Further, the wide-angle lens 100 satisfies all of the following conditions (1), (2), and (3). First, as the condition (1), the Abbe number ν1 of the first lens 10, the Abbe number ν2 of the second lens 20, and the Abbe number ν3 of the third lens 30 all exceed 50. More specifically, first, the first lens 10 has an Abbe number ν1 of 58.0 and a refractive index of Nd of 1.491. The second lens 20 has an Abbe number ν2 of 55.8 and a refractive index of Nd of 1.531. The third lens 30 has an Abbe number ν3 of 55.8 and a refractive index of Nd of 1.531. Therefore, the Abbe number and the refractive index satisfy the following conditions.
Abbe number 1st lens 10> 2nd lens 20 = 3rd lens 30> 50
Refractive index Nd
1st lens 10 <2nd lens 20 = 3rd lens 30

Further, the radius of curvature R12 (mm) at the center of the lens surface (second surface 2) located on the image side of the first lens 10 and the center of the lens surface (third surface 3) located on the object side of the second lens 20. The radius of curvature R21 (mm) and the focal length f0 in the above satisfy the following condition (2).
Condition (2): -5 <(R12 x R21) / f0 <-2

More specifically, the radius of curvature R12 at the center of the lens surface (second surface 2) located on the image side in the first lens 10 is 1.950 mm, and the lens surface located on the object side in the second lens 20 (second surface 2). Since the radius of curvature R21 at the center of the third surface 3) is -3.957 (mm) and the total focal length f0 is 2.112 mm, (R12 × R21) / f0 is -3.65. , The above condition (2) is satisfied.

Further, the distance between the center of the lens surface (first surface 1) located on the object side of the first lens 10 and the center of the lens surface (fourth surface 4) located on the image side of the second lens is da (mm). When the distance da is 6.59 mm, the following condition (3) is satisfied.
Condition (3): 1 <da / f0 ≤ 3.226
Meet.

As described above, the wide-angle lens 100 of this embodiment has a lens configuration of three elements in three groups, and the three lenses are made of plastic. Therefore, the cost of the wide-angle lens 100 can be reduced and the weight can be reduced. Further, in the present embodiment, the Abbe number ν1 of the first lens 10, the Abbe number ν2 of the second lens 20, and the Abbe number ν3 of the third lens 30 all exceed 50, satisfying the condition (1). Therefore, the color dispersion is small. Moreover, since the second lens 20 is a meniscus lens, the axial chromatic aberration is canceled by the surface on the object side (third surface 3) and the surface on the image side (fourth surface 4) in the second lens 20. Therefore, the same effect as that of the first embodiment is obtained, such as the small axial chromatic aberration of the wide-angle lens 100.

[Other embodiments]
In the first, second, and third embodiments, both sides of the second lens 20 and the third lens 30 are aspherical, but in one or both of the second lens 20 and the third lens 30, only one side is aspherical. May be.

In the above embodiment, the Abbe number ν1 of the first lens 10 is 58.0, and the Abbe numbers ν2 and ν3 of the second lens 20 and the third lens 30 are 55.8, but as a result of various studies, the Abbe number is 55.8. The numbers ν1, ν2, and ν3 are not limited to the above values, and if they exceed 50, sufficient axial chromatic aberration can be obtained as a wide-angle lens 100 used for an interphone of a front door.

10 ... 1st lens, 20 ... 2nd lens, 30 ... 3rd lens, 40 ... Aperture, 100 ... Wide-angle lens

Claims (4)

It consists of a first lens, a second lens, an aperture, and a third lens arranged in order from the object side.
The first lens is a negative meniscus lens in which at least one surface is aspherical and a convex surface is directed toward an object.
The second lens is a positive meniscus lens in which at least one surface is aspherical and the convex surface is directed toward the image side.
The third lens is a positive lens in which at least one surface is aspherical, the convex surface is directed to the object side, and the convex surface is directed to the image side.
When the Abbe number of the first lens is ν1, the Abbe number of the second lens is ν2, and the Abbe number of the third lens is ν3, the Abbe numbers ν1, ν2, and ν3 all exceed 50 .
When the distance between the center of the lens surface located on the object side of the first lens and the center of the lens surface located on the image side of the second lens is da (mm), the distance da is the following conditional expression.
1 <da / f0≤3.226
A wide-angle lens characterized by satisfying . The radius of curvature at the center of the lens surface located on the image side of the first lens is R12 (mm), and the radius of curvature at the center of the lens surface located on the object side of the second lens is R21 (mm). When the focal length is f0 (mm) and the lens surface is a convex surface protruding toward the object side or a concave surface recessed toward the object side, the radius of curvature R12 and the radius of curvature R21 are set to positive values, and the lens surface is set. When is a convex surface protruding toward the image side or a concave surface concave toward the image side, when the radius of curvature R12 and the radius of curvature R21 are negative values, the radius of curvature R12, the radius of curvature R21, and the whole The focal length f0 is the following conditional expression −5 <(R12 × R21) / f0 <-2.
The wide-angle lens according to claim 1, wherein the wide-angle lens satisfies the above. The wide-angle lens according to claim 1 or 2 , wherein both the second lens and the third lens are aspherical in both the lens surface located on the object side and the lens surface located on the image side. .. The wide-angle lens according to any one of claims 1 to 3 , wherein the horizontal angle of view is less than 100 deg.

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